Cracks are naturally formed during the creep deformation of the rock. When a crack from the side of a rock is hit by an additional load, the crack starts to grow in the direction of the applied force. If the load is not as strong, a slow crack will be brought to closure very soon. On the other hand, if the load is very strong, the stress concentration will induce an accelerated crack growth. When the crack has grown to an extent that a stress concentration at crack tips results in an increase of the nucleation stress, the stress concentration will be enhanced, which, in turn, will cause further crack growth. In the left panel of this figure, once the stress load is larger than the threshold value, this will induce crack growth. Nucleated and new cracks will grow faster than the grown cracks so that the entire stress field will gradually evolve into the stress field shown in the right panel of this figure. If the loading is large enough, the crack will grow into the depth, and then, a shear fracture is induced. And the system will extend the dislocation network by creating at the fracture surface a new configuration of dislocation.
However, if the strain field is on the safe side, a shear fracture will not be induced. The strain field at the tip of the tip-loaded crack can be seen in this figure; the real crack propagation direction can be clearly seen on the left-hand-side edge of the yellow lattice.
I need to start by restating something that I said earlier: ABB does not make computer systems. Once you realise that we make industrial equipment, for instance drives, you can see why ABB Systems is always trying to merge the electronics and infrastructure sides more than ever before. But that makes sense: ABB has already sold the majority of its home consumer electronics gear (audio, video, etc.), and to the extent it is making a stand in telecommunications, it is approaching the consumer from a different angle. ABB really doesn't want to sell telecom, as you know if you keep reading this. They want to sell you power over your home and business. d2c66b5586